| 摘要 |
PURPOSE:To eliminate the influence causced by external objects and to enable correct decision, by changing and detecting the frequency of the ultrasonic wave which is made incident toward the wall of a vessel. CONSTITUTION:An ultrasonic wave is generated by an ultrasonic wave sensor 1 for transmission in accordance with the signal of the device in a signal transmission system, and is propagated to a vessel 10 through a wedge 2. If no water exists on the outside surface of the vessel 10, the wave is propagated in the vessel 10 and is detected by a signal reception system. On the other hand, if there is liquid 11 and if there is an object 13 in proximity thereto, the wave passes through the liquid 11, and comes back by reflecting on the object 13. If the phase of the oscillation of the reflected wave B coincides with the phase of the wave A propagated in the wall of the vessel 10, both waves intensify each other and the level of the signal increases. Conversely, when both waves deviate by 180 deg., the waves offset each other and the level of the signal decreases. When the frequency is changed, the way of off setting or intensifying differs from each other and the level of the received signal changes. Such change does not arise unless the liquid 11 exists; therefore, the presence or the absence of the liquid 11 is known by whether the received signal has a difference in level or not. |
